Direct indicating devices for measuring respiratory resistance

ABSTRACT

A flow resistance chamber through which a person breathes has a flow resistance which can be rapidly switched between two values of resistance. The pressure differential across the resistance is measured, and the electrical output of the pressure difference measurement is switched between two storage circuits in synchronism with the switching of the flow resistance. This switching is done for a period that is short compared with the breath cycle. The quotient of the two pressure differences registered in the storage circuits is continuously formed and displayed on an indicator or recording.

United States Patent 91 Hampl [541 DIRECT INDICATING DEVICES FOR MEASURING RESPIRATORY RESISTANCE [75] Inventor: Franz Hampl, Hoechberg, Germany v [73] Assignee: Erich Jaeger, Wurzburg, Germany 22 Filed:- June 5,1973

21 'Appl. No.: 367,344

Related U.S. Application Data [63] Continuation of Ser. No. 129,678, March 31, 1973,

abandoned.

[52] U.S. Cl...., 128/2.08 [51] IntLCl A61b 5/08 [58] Field of Search... 128/207, 2.08, 2 R, DIG. I7

[56] References Cited 7 UNITED STATES PATENTS 3,036,569 5/1962 Clements et a1. 128/208 3,559,638 2/1971 Potter 128/208 3,621,833 11/1971 Crane 128/208 FOREIGN PATENTS OR APPLICATIONS 1,119,459 12/1961 Germany 128/208 850,750 10/1960 Great Britain 128/208 Dec. 31, 1974 OTHER'PUBLICATIONS .lourn. Of Clinical Investigation, Vol. 38, No. 7, pp. 1262-1270, July 1959. 1 .lourn. of Applied Physiology, Vol. 8, pp. 587-594, May 1956. a

Primary Examiner-Kyle L. Howell Attorney, Agent, or Firm-Flynn & Frishauf l5 7] ABSTRACT A flow resistance chamber through which a person breathes has a flow resistance which can be rapidly switched between two values of resistance. The pressure differential across the resistance is measured, and the electricaloutput of the pressure difference measurementis switched between two storage circuits in synchronism with the switching of the flow resistance.

This switching is done for a period that is short compared with the breath cycle. The quotient of the two pressure differences registered in the storage circuits is continuously formed and displayed on an indicator or recording.

7 Claims, 2 Drawing Figures DIRECT INDICATINC DEVICES FOR MEASURING RESPIRATORY RESISTANCE example Zeitschrift fur Aerosol-Forschung und -Thera- 1 pie, second year, issue 4, August 1953, pages 475 to 484) is a method for determining the flow resistance of respiratory air passages of the human body (breath resistance).vlt constitutes a further development of the so-called partial interruption method, which is based on the following considerations: The breath resistance R,, is obviously equal to the difference between the alveolar pressure P (pressure in the alveoli) and the ambient pressure Py divided by the flow F (amount of air breathed in or out per unit time). The flow F is in practice measured by means of a so-called pneumotachograph responding to the pressure drop at a resistance to flow arranged in an air passage external to the patients body.

The alveolar pressure I, cannot be directly measured; If, however, a rapid closure blocking valve is placed in the external air passage to interrupt the respiv rationair flow for a short time, the same pressure (interruption pressure) becomes established on the proximal side, that is to say on the lung side of the valve as exists in the alveoli, because, owing to the absence of flow there is then, no pressure drop in the air passages in the patients body. Since the process of pressure equalization between the alveoli and either the mouth of the person investigated or the proximal pressure sensing device of the pneumotachograph occurs more rapidly than any substantial compression or expansion of trapped air owing to the respiratory action, the interruption pressure in practice agrees with the alveolar pressure to a large extent.

The complete interruption of the respiratory air current, however, often leads to disturbances in the respipressure method developed by Dirnagl on the basis of the interruption pressure method, however the respira-' tory air current is no longer completely interrupted and instead only a partial interruption is produced. In practice this is carried out by causing the person to be investigated to breath through a resistance to flow, whose magnitude can be switched over between two values.

Respiratory resistance measuring devices which function in accordance with the Dirnagl partial interruption pressure method are described, for example, in the German specifications Nos. 1,029,526 and 1,1 19,459 and provide measurements which constitute a valuable addition to measurements obtained with the body plethysmograph (see for example the German specification No. 1,466,840).

One aim of the present invention is to provide a device, operating on the partial interruption pressure method, for measuring respiratory'resistance which provides an output signal which constitutes a measure for the respiratory resistance and therefore does not require any further processing.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a direct indicating device for measuring respiratory resistance, comprising a flow resistance through which respiratory air is to pass and which can be switched over by a control device between two resistance values, and also a differential pressure sensing device which is connected on both sides of the flow resistance and provides an electrical 0 output signal corresponding to the pressure drop at the flow resistance. The output of the pressure sensing means can be switched selectively to either of two signal storage circuits, each of which can store a a signal corresponding to the instant value of the output signal of the pressure sensing means as long as they are coupled with the output of the pressure sensing meansqThe storage circuits hold the last signal value stored as long as they are disconnected by the switch from the output of the pressure sensing means. The switching over deby a timing device so that the signals in each storage device respectively relate specifically to one of the flow resistance conditions. The two signal storage circuits,

finally, are connected with a dividing circuit, which forms a quotient signal corresponding to the quotient of the signals stored by the respective signal storage circuits. Means are provided for feeding the quotient signal to an indicating and/or registering device.

In the case of breathing in (inspiration), the pressure sensing device provides an output signal whose polarity is opposite to that in .the case of breathing out expiration. In accordance with a further feature of the invention, therefore, a circuit arrangement, for example a rectifying circuit or a switch controlled in accordance with the polarity of the output signal of the pressure sensing device, is provided which ensures that a signal is provided to the signal Switch only during breathing in or only during breathing out, whichever is selected or designed in the circuit. Preferably the signal is provided to the switch 16 only during breathing out.

An illustrative embodiment of the invention is described below in conjunction with the accompanying drawing, in which:

FIG. 1 is a diagrammatic view of a direct indicating device according to the invention for measuring respiratory resistance, and

FIG. 2 is a graph of pressure drop against time as measured in operation of a device in accordance with FIG. 1. v

The direct indicating respiratory resistance measuring device shown in FIG. 1 comprises a flow resistance, which can be switched over between two resistance values, housed in a flow resistance chamber 10. Flow resistances of the type shown are described for example in the above-mentioned German specifications Nos. 1,029,526 and 1,119,459, to which express reference is made so that a detailed description of them is not required.

The flow resistance chamber 10is connected with a differential pressure sensing means 12, which supplies an output signal corresponding to the pressure drop across the flow resistance, via an amplifier 14 to a switch 16. The switch has two positionsand connects the amplified output signal of the pressure sensing means 12 selectively with one of the two signal storage circuits 18a and 18b, which store a signal as further described below. The stored signal thus follows the output signal of the pressure sensing means 12 as long as the latter is connected with the related signal storage circuit 18 and then remains at the last-stored signal value when the connection between the pressure sensing means and the signal storage circuit concerned is interrupted by the switch 16.

Each signal storage circuit can, as is indicated for example at the bottom of FIG. 1 in the rectangle 18 in broken lines, have a differential amplifier 19, a capacitor C and a resistor R, which are connected in the manner described. As shown in the diagram, one input of the differential amplifier 19 is used for a feedback connection.

The outputs of the signal storage circuits 18 are connected with a dividing circuit 20, whose output 22 provides an output signal corresponding to the quotient of the supplied signals. The output signal can be supplied to an indicating device, for example an oscilloscope or a registering device such as a plotter 24. The registering device can be calibrated directly in units of breath resistance R The flow resistance switch-over device denoted by an arrow 26 drawn in broken lines, and the actuating device for the switch 16 are coupled with a common timing means 28, which switches over the flow resistance and the switch 16 synchronously. The switching over is preferably carried out periodically with a frequency which is substantially greater than the frequency of breathing.

In operation a person 30 to be examined breathes through the flow resistance 10 by means of a mouth piece or a mask (not shown), so that the respiratory air flows through the resistance. When the flow resistance 10 has been set at its greater resistance value, the pressure drop AP runs in accordancewith the curve A in FIG. 2, which has the greater swing about the horizontal graph axis and is partially drawn in full lines and partially in interrupted lines. When the flow resistance has its smaller value, the pressure drop varies in accordance with the curve B which is partly in the form of dots and is nearer to the horizontal graph axis. When the resistance to respiratory air is periodically switched over between its two resistance values, the pressure drop across the flow resistance it) varies in accordance with the full lines drawn in FIG. 2, with generally rectangular pulses, comprising parts of curves A and B.

In operation the flow resistance and the switch 16 are switched over synchronously, preferably periodically. The signal storage circuits 18a and 18b then respectively store the signal values which correspond to the curves A and B. In the time interval between t, and t the signal storage circuit 18b is for example connected with the output of the differential pressure sensing means 12 and at the time t: it stores a signal in accordance with AP Simultaneously with the switching over of the resistance value the switch 16 switches of the output of the amplifier 14 from the signal storage circuit 18b and connects it with the signal storage circuit 18a, which now in the time between t and t stores a signal corresponding to the pressure difference AP The dividing circuit 20 continuously forms a quotient signal corresponding to the quotient of the signals stored in the signal storage circuits 18a and 18b, i.e., a signal corresponding to AP /AP which is recorded by the registering device 24 (possibly after smoothing by a low pass filter not shown). The recording then indicates the variation in time of the respiratory resistance during breathing. If the vertical axis of the recording is calibrated in values of R no further evaluation is needed.

The signal transfer path between the flow resistance and the recording or indicating device can comprise a switching member which ensures that the respiratory resistance R is only recorded and/or indicated during one breathing phase, for example only during breathing out. For this purpose a rectifying circuit 32, for example, is all that is required between the differential pressure sensing means 12 and the amplifier 14 (or between the latter and the switch 16).

If the respiratory resistance is to be measured both during breathing in and also during breathing out, the pressure sensing means 12 and the switch 16 can have a twin path rectifier circuit connected between them.

I claim:

1. A direct indicating device for continuously measuring the internal resistance of a persons respiratory system comprising:

a flow resistance chamber having a connection adapted for the persons mouth or nose and a connection to the atmosphere and having an interposed variable resistance means, switchable between two finite values of resistance, through which air breathed by said person through said mouth or nose connection must pass;

flow resistance switching means operatively connected with said variable resistance means for switching said resistance means between said two values of resistance;

pressure sensing means connected to said chamber and responsive to the pressure difference across said flow resistance means and including means for providing an electrical output representative of said pressure difference;

two electrical storage means for storing differential pressure output signals of said pressure sensing means respectively related to said two resistance values, each of said storage means having an input and an output connection and includes means capable of following a signal provided to said input connection and of storing the last value of the sig nal so provided when said input connection is disconnected from said pressure sensing means;

signal switching means synchronized with said flow resistance switching means arranged for alternately connecting each of said storage means to said electrical output of said pressure sensing means;

timing means including means for causing repetitive back-and-forth operation, in synchronism, of said flow resistance switching means and for said signal switching means at intervals short compared with a persons normal breathing cycle;

quotient producing means responsive to the respective signals present in said two storage means, and

indicating means responsive to said quotient producing means for continuously indicating respiratory resistance of said person during at least one direction of breathing,

said indicating means being capable of and arranged for responding to variations of the output of said quotient producing means within any unidirectional breath flow period of the persons breathing cycle.

2. A direct indicating device for continuously measuring'respiratory resistance as defined in claim 1 in which:

flow direction responsive means are interposed in the signal path between said pressure sensing means and said signal switching means for switching off the signal supplied to said signal switching means during periods of breath flow in one direction of breathing.

3. A direct indicating device for measuring'respiratory resistance as defined in claim 1, in which:

a path rectifying means is interposed in the signal path between said pressure sensing means and said signal switching means and is arranged to switch the polarity of the output signal of said pressure sensing means or of a signal derived therefrom, so that the polarity of the output of said quotient producing means will remain the same regardless of direction of respiratory air flow through said flow resistance chamber.

4. A direct indicating device for continuously measuring respiratory. resistance as defined in claim 1 in which said storage means includes means for rapid setting of the storage level therein during alternate switching intervals of said signal switching means to a new value of said electrical output of said pressure sensing means, in the event of change of such value, and includes means for maintaining the storage level therein substantially constant during the other switching intervals of said signal switching means.

5. A direct indicating device for continuously measuring respiratory resistance as defined in claim 2 in which said storage means includes means for rapid setting of the storage level therein during alternate switching intervals of said signal switching means occurring during periods of breath flow in the direction of breathing for which said flow direction responsive means does not switch off the signal supplied to said signal switching means, such setting of said storage level being then effected to a substantially momentary value of said electrical output of said pressure sensing means, and in which during other switching intervals of said signal switching means, said storage means includes means for maintaining the storage level substantially constant.

' playing with brief persistance the respiratory resistance of a patient, at least during periods of breath flow in one direction of breathing.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 9 Patent No. 3,857,385 Dated December 31, 1974 lnventofls) Franz HAMPL It is certified that error appears in the above-identified patent Q and that said Letters Patent are hereby corrected as shown below:

On the cover page, first column, following item [63] entitled "Related U.S. Application Data", insert [30] Foreign Application Priority Data A April 3, 1970 Germany P 2O 16 073.0

Signed and Sealed this thirteenth Day of April1976 [SEAL] Arrest:

6 RUTH c. MASON c. MARSHALL DANN AIM-Wing OIL/7v? (mnmissl'mwr oj'lareitls and Trademarks 

1. A direct indicating device for continuously measuring the internal resistance of a person''s respiratory system comprising: a flow resistance chamber having a connection adapted for the person''s mouth or nose and a connection to the atmosphere and having an interposed variable resistance means, switchable between two finite values of resistance, through which air breathed by said person through said mouth or nose connection must pass; flow resistance switching means operatively connected with said variable resistance means for switching said resistance means between said two values of resistance; pressure sensing means connected to said chamber and responsive to the pressure difference across said flow resistance means and including means for providing an electrical output representative of said pressure difference; two electrical storage means for storing differential pressure output signals of said pressure sensing means respectively related to said two resistance values, each of said storage means having an input and an output connection and includes means capable of following a signal provided to said input connection and of storing the last value of the signal so provided when said input connection is disconnected from said pressure sensing means; signal switching means synchronized with said flow resistance switching means arranged for alternately connecting each of said storage means to said electrical output of said pressure sensing means; timing means including means for causing repetitive back-andforth operation, in synchronism, of said flow resistance switching means and for said signal switching means at intervals short compared with a person''s normal breathing cycle; quotient producing means responsive to the respective signals present in said two storage means, and indicating means responsive to said quotient producing means for continuously indicating respiratory resistance of said person during at least one direction of breathing, said indicating means being capable of and arranged for responding to variations of the output of said quotient producing means within any unidirectional breath flow period of the person''s breathing cycle.
 2. A direct indicating device for continuously measuring respiratory resistance as defined in claim 1 in which: flow direction responsive means are interposed in the signal path between said pressure sensing means and said signal switching means for switching off the signal supplied to said signal switching means during periods of breath flow in one direction of breathing.
 3. A direct indicating device for measuring respiratory resistance as defined in claim 1, in which: a path rectifying means is interposed in the signal path between said pressure sensing means and said signal switching means and is arranged to switch the polarity of the output signal of said pressure sensing means or of a signal derived therefrom, so that the polarity of the output of said quotient producing means will remain the same regardless of direction of respiratory air flow through said flow resistance chamber.
 4. A direct indicating device for continuously measuring respiratory resistance as defined in claim 1 in which said storage means includes means for rapid setting of the storage level therein during alternate switchIng intervals of said signal switching means to a new value of said electrical output of said pressure sensing means, in the event of change of such value, and includes means for maintaining the storage level therein substantially constant during the other switching intervals of said signal switching means.
 5. A direct indicating device for continuously measuring respiratory resistance as defined in claim 2 in which said storage means includes means for rapid setting of the storage level therein during alternate switching intervals of said signal switching means occurring during periods of breath flow in the direction of breathing for which said flow direction responsive means does not switch off the signal supplied to said signal switching means, such setting of said storage level being then effected to a substantially momentary value of said electrical output of said pressure sensing means, and in which during other switching intervals of said signal switching means, said storage means includes means for maintaining the storage level substantially constant.
 6. A direct indicating device for continuously measuring respiratory resistance as defined in claim 2 in which said indicating means is a means for visually recording respiratory resistance as a function of time at least during periods of breath flow in one direction of breathing.
 7. A direct indicating device for continuously measuring respiratory resistance as defined in claim 2 in which said indicating means is a means for visually displaying with brief persistance the respiratory resistance of a patient, at least during periods of breath flow in one direction of breathing. 